The present study tries to evaluate the diagnosit value in malignant hepatic tumors of polyamines, of which the relationship with cellular kinetics is known, and histamine, of which catabolism follows a similar pathway. One hundred and fifty six patients were studied: 53 with malignant liver tumors (27 primary, 26 metastatic) and 103 with non-tumoral liver diseases of which 65 were cirrhotic and 38 non-cirrhotic. Erythrocyte polyamines (spermidine and spermine) and histamine levels were assayed. The results indicate the following. 1. Polyamine levels were significantly increased (a) in cirrhotic patients, not only when compared with controls (p less than 10(-8)), but also when compared with the non-cirrhotic patients (p less than 10(-7)); (b) in primary malignant hepatic tumors (p less than 10(-3)). 2. Histamine was significantly increased (a) in the non-tumoral liver diseases (p less than 10(-4)), but with no difference between cirrhotic and non-cirrhotic patients; (b) in the secondary malignant tumor patients, histamine levels were lower than in primary tumor patients (p less than 0.04). 3. There was no correlation, in all groups studied, between polyamine and histamine levels. These results suggest the following practical implications. 1. For non-tumor liver diseases, appreciably increased polyamine levels may represent a further argument favoring a cirrhotic condition. 2. In diagnosing hepatic scintigraphic defects, increased polyamine levels would suggest a primary malignant hepatic tumor; low histamine levels are more in favor of a secondary malignant hepatic process.